Apparatus for induction heating



June 24, 1958 w. A. EMERSON HAL 2,840,677

APPARATUS FOR INDUCTION HEATING Filed May 15, 1956 United States PatentO APPARATUS FOR INDUCTION HEATING William A. Emerson, William B. Brown,and Clarence A. Kuhne, Baltimore, Md., assignors to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application May 15, 1956, Serial No. 585,040

6 Claims. (Cl. 219-10.67)

This invention relates to induction heating apparatus, and moreparticularly to an induction furnace for heating tubular articles 'byinducing alternating currents in the walls of the article.

In the industrial arts it has been found desirable to heat large blanksfor forging and the like in a time of often less than one minute. Highfrequency induction heating has been widely used but has been founddisadvantageous for the heating of large thick tubular bodies in thathigh frequency inherently heats the metal at the external surface of theworkpiece while that below the surface remains relatively unheated.

In the use of low frequency induction heating diiculty has beenencountered in locating a laminated iron core closely adjacent to theworkpiece so as to reduce the reluctance of the magnetic path with aconsequent reduction in impedance of the coil so as to increase powertransfer to the work. Diculties in workpiece positioning with respect tothe laminated core have in the past precluded low frequency heating.

It is an object of this invention to provide an improved inductionheating apparatus for heating the side walls of tubular metallicarticles.

It is another object to provide apparatus for rapid and i eicient massproduction induction heating of large work- It is a further object toprovide induction heating apparatus for the purposes described in whichportions of a magnetic core are adapted to be relatively moved andreplaced automatically for insertion of a workpiece therebetween.

It is a still further object to provide induction heating apparatushaving an open-core transformer for the purposes described in whichpower factor and eiliciency are improved and exciting current is reducedby provision of movable flux concentrating means associated with thetransformer core.

It is an additional object to provide heating apparatus of the typedescribed for obtaining a controlled predetermined heat pattern inspecified areas of a workpiece to be forged or otherwise worked.

A different object of this invention is to provide an automaticinduction furnace for heating selected portions of substantiallycylindrical tubular workpieces in which a plurality of individual fluxconcentrating magnetizable members are adapted to be moved into areluctance decreasing and flux concentrating position simultaneouslywith movement of workpieces into an inductive relation with the heatingcoil of a furnace.

A still different object of this invention is to provide automaticapparatus of the type described in which a rst elevator mechanism isreciprocally operative to elevate a workpiece from a delivery positionto an induction heating position within a furnace coil and to remove theworkpiece when heating is completed, and in which a second elevatormechanism is operative to reciprocally position a plurality of fluxconcentrating members in a first position and a second position, saidfirst position being Patented June 24, 1958 adjacent to the transformerand adjacent to the positioned of the core structure.

workpiece, said second position being relatively far removed from saidtransformer and substantially removed from said workpiece whereby saidworkpiece may be readily conveyed horizontally away from said furnace.

These and further objects will be apparent from the followingdescription taken in accordance with the accompanying drawing,throughout which like reference characters indicate like parts, whichdrawing forms a part of this application and in which:

Figure l is a partial vertical longitudinal section taken along adiameter of a furnace according to the invention showing diametricallyopposed core members in section and further showing the workpiece andflux concentration elevating mechanisms in solid lines in the elevatedposition and in broken lines in the descended or retracted position; and

Fig. 2 is a transverse horizontal section through one semi-cylindricalhalf of the furnace, taken along the line II-II of Fig. 1.

For convenience in describing the relative positions of the variousparts of the apparatus, it will herein be thought of as standing inanupright position, as in the preferred embodiment, with the furnaceinductor coil having its axis vertically aligned as indicated in Fig. l,but it is to be understood that in actual practice the said axis may bepositioned horizontally or in an inclined position.

A core structure for the furnace comprises a plurality of elongatedvertical inner members 4 disposed within the work path and within thecylindrical workpiece 6. The inner core members 4 are not individuallycoaxial with the work path but are disposed in spaced relation aboutthat `axis so that the inner core group is coaxial to the work path,workpiece 6 and coil 8.

The outer core structure 10 comprises a plurality of laminatedmagnetizable core members 12 each having a vertical leg portion disposedclosely adjacent the outer periphery of the coils and having upper legportions 14 and lower leg portions 16 extending radially inward adjacentthe top and bottom ends of the coil 8. The upper leg portion 14 extendsinwardly a substantial distance beyond the inner diameter of the coil 8thereby approaching in close proximity to the outward side of thecorresponding inner core member 4 to eliminate any appreciable air gapat the upper end of the inner cores. The lower horizontal core legmember 16 is of lesser length, extending only slightly beyond the innerdiameter of the coil 8, and terminating short of the work path diameter.A space or air gap is thus provided between the inner end of the lowerhorizontal leg portion 16 and the inner core member 4 through which theworkpiece 6 may be longitudinally inserted and positioned with sidewalls7 lying adjacent to the inner diameter of coils 8.

The plurality of laminated outer core members 12 together with theirrespective inner core members 4 provide a plurality of magneticallyparallel ilux paths threading axially through the inner core members 4positioned in the hollow center of the workpiece 7, across an air gap 18(discussed hereinafter) at the lower end of the core member 4 radiallyoutward through the lower horizontal leg portion 16 and thencevertically upward and radially inward through core members 12. The onlysubstantial discontinuity or high reluctance portion of the magnetic uxpath is the air gap 18 between the inner end of the lower leg members 16and the lower end of core member 4. This gap 18 is necessarily providedin order to allow insertion of the workpiece sidewalls 7 into the spacebetween the inner diameter of the coil 8 and the outer diameter of theinner core assembly.

The separate outer and inner vertical core members 4 and 12, asdescribed, comprise a preferred embodiment It is intended that othersuitable configurations of the magnetic core may be satisfactorilyemployed. For example the core structure may conrprise a plurality ofsubstantially U-shaped core members individually straddling theperiphery of the coil 8, with one leg of the U-shaped member extendingvertically downward outside the coil and with the other leg portionextending downward inside the 'annular workpiece passageway.

In the form of the invention shown in the drawings the induction coilsare of the 6() cycle 460 volt type comprisg ing large diameter separatecoil sections. Each coil section 8 is insulated from the next bytransite insulator rings Ztl of flat annular configuration having adiameter slightly greater than that of the coil S. Each section of thecoil is of the flat spiral wound type comprising a plurality of turns ofround or rectangular tubing of conductive metal such as copper oraluminum. Each spiral coil 8 has end leads extending radially andarcuately outward from the coil at one side to an insulating terminalboard. By virtue of appropriate connectors provided on the terminalboard, various interconnections of the spaced coil sections may be made.To achieve various predetermined heat patterns dilferent coil sectionsmay remain disconnected from any power source as desired, or may beconnected in various permutations of series and parallel combinations.

While in the disclosed embodiment the coil is intended for 60 cyclesingle phase operation, it is evident that the apparatus may be adaptedfor other frequencies, voltages and numbers of phases in the lowfrequency power spectrum without departing from the scope of theinvention.

Further provided on the terminal board are appropriate connectors forcirculating coolant fluid through the separate coil sections. Water (orother coolant) may be supplied to the various coils from a common sourcethrough insulating fluid-tight tubing. In addition to fluid cooling, thecoils 8 are further protected from the heat of the internally adjacentworkpiece 6 by means of a coating 22 of refractory cement such asSillimanite No. ,lOl (manufactured by Charles Taylor Sons Co.,Cincinnati), or the like applied over the horizontal transite rings 20and the inductor coils 8 on the inside of the coil assembly where thecoils face the hot workpiece 6.

The transformer core and coil assembly is located at a convenientelevation from the floor for operation with suitable conventional rolleror belt conveyors (not shown) for delivery and removal of workpieces 6.The support structure 25 is provided with a horizontal planar table top27 having a central opening 29 disposed in spaced relation below thefurnace assembly. The support structure 25 for the furnace assemblyconveniently comprises four vertical corner posts 31 to the top of whichis mounted a substantially planar furnace support plate 33 having acentral opening 35 slightly larger than the internal diameter of theheating coil assembly. Circum#Y ferentially spaced around the centralopening 35 are vertically and upwardly extending channel members 37rigidly attached at the lower ends to the furnace support plate 33. Theouter core members 12 of the furnace are supported on the channelmembers 37 by through-bolts or other appropriate fastening means so asto be rigidly located in vertical positions circumferentially spacedaround the work path opening in the furnace support plate 37. Y

The respective central openings 29 and 37 in the planar table top 27 andin the furnace support plate 33 are aligned vertically with theircentral axis being coincident with the central axis of the furnaceinductor coil 8 andV Disposed below the table top 2,7 within therectangularV support structure 25 is an elevating mechanism preferablycomprlsing a pneumatic or hydraulically operated cylinder 41, piston andpiston rod 43. However, it is understood that other suitable elevatingmechanisms may be satisfaci torily employed. Appropriate electricallyoperated valves, relays, pressure switches, and circuitry are providedfor automatic cyclical operation of the fluid operated elevator 39 insynchronism with delivery of workpieces to the work path from anexternal conveyor. The iiuid operated elevator 39 is preferably disposedin a vertical position in alignment with the axes of the furnace 10 andwork path. Rigidly mounted on the upper end of the elevator piston rod43 is a planar elevator platform 45 of a diameter less than that of theopening 35 in the furnace support plate 33 so that the platform 45 isadapted to substantially close the furnace support plate opening 35 whenthe elevator is in the raised or heating position.

The primary function or purpose of the elevator platform 45 is tomovably support a plurality of preferably laminated magnetizable iluxconcentrating core pieces 47. The said core Vpieces 47 are rigidlymounted on the platform 45 in circumferentially spaced positionsinwardly adjacent to the periphery of the platform 45. In the centralportion of the platform 45 is located a superstructure comprising aworkpiece carrier plater49 for supporting a workpiece 6 above the planeof the principal Yele-v vator platform 45. The workpiece support plate49 is connected for vertical movement relative to the elevator platform45 by means of a plurality of spaced slide-bolts 51 rigidly attached tothe workpiece support plate 49 and verticallyslidable in openings in theelevator platform 45. Enlarged heads 53 are provided at the lower end ofthe slide bolts 51 Vso that the bolts 51 and the support plate 49 arecaptively Ebut movably connected to the elevator platform 45. Thesupport plate 49 is thus freely movable for a relatively short distancetoward and away 4from the elevator platform 45.

Beneath the tabletop 27 and spaced slightly below the lowermost positionof the elevator platform 45 is a planar stop plate 55 adapted to engagethe heads`53 of the slide boltsvSl as the elevator platform 45approaches the retracted position. When the slide bolt heads 53 contactthe stop plate 55, further downward motion of the workpiece supportplate 49 is prevented while the elevator platform 45 continues todescend. The flux concentrating core members 47 are thus retracted awayfrom the curved side portions 9 of the workpiece 6 and below thetabletop 27 whilethe workpiece support 49 terminates its downward motionwhen substantially coincident with the table top 27.

At the beginning of the operative cycle a workpiece 6 is conveyedhorizontally into approximately the center of the table top 27 by anexternal conveyor (not shown). A suitable switch is automaticallyoperated by delivery of the workpiece 6 to initiate operation of theiluid operated elevator 39. As the elevator platform 45 begins toascend, the tapered ends of the flux concentrator core members 47 risethrough the annular opening surrounding the workpiece carrier 49. If, asin the usual case, the workpiece 6 is not accurately centered, thetapered ends of core members 47 will joggle the lower end' of theworkpiece V6 until reasonably accurate centering is achieved. As theelevator platform 45 continues to rise, annular spacers 57 on the slidelbolts 51 will engage the upper surface of theY platform 45 so that theworkpiece carrier 49 will thereafter be supported by and will movetogether with the platform 45. The platform 45 then continues to ascenduntil the workpiece 6 is wholly within the peripheral outer core members12r and the iiux concentrator core pieces 47 are laterally adjacent tothe endsso as to reduce the required exciting current, increase the.

power rfactor andV increase overall e'ciency oftheinduc tor furnace.Inone instance of an apparatus havingrnov` .5 able tiux concentratingcore pieces of the type described, a 500 kva. furnace was improved asfollows:

In addition, it was Ifound that power loss in the transformer coil 8 wasreduced by 14% thereby reducing the normally present deleterious heatingof the coils and insulation.

In one embodiment for applying the apparatus shown in Fig. 1, a systemis provided using two identical furnaces of the type described.Automatic loading devices are provided for delivery' of workpieces froma single gravity roller conveyor to the work paths of both furnaces.Control circuits for the two furnaces are electrically interconnected toprovide for alternate energization of the primary induction coils. Theoperating cycle of the tandem system is as follows.

The first loading device loads a workpiece 6 into the first furnace workpath on the workpiece support plate 49. As soon as the workpiece is inposition underneath the heating coils 8, the iiuid operated elevatingcylinder 39 is energized. Premature energization of the elevatingmechanism is prohibited by workpiece actuated switches which determinethat the workpiece is properly positioned. Upon energization of theelevator 39 the workpiece 6 ascends into the heating coil 8 of the lirstfurnace; a pressure operated switch, responsive to the uid pressure inthe cylinder, energizes a conventional timer and a line contactor toapply power to the heating coil for a predetermined interval.Simultaneously with energization of the first heating coil, a loading`device associated with the second furnace is energized and operates toload a workpiece on the workpiece carrier plate 49 of the secondfurnace. During the heating time interval for the first furnace, theelevator of the second furnace operates to position the workpiece in thecoil in position for heating. As soon as the timed heating interval inthe lirst furnace is complete, the input power is immediatelytransferred over to the coil of the second furnace. The tirst furnaceelevator automatically descends and the heated workpiece is dischargedto an external conveyor. The first loading device is then automaticallyoperated to load a second workpiece on the first furnace carrier plate.When the timed heating interval of the second coil expires the rstfurnace elevator is in the ascended position and power is immediatelytransferred from the second heating coil to the first heating coil andrepetition of the tandem working cycle begins.

By virtue of the above described synchronous operation of a pair ofheating furnaces, a continuous flow of power from an external system ismaintained. Uninterrupted power consumption, as described, is highlyadvantageous in that variable loading and transient conditions arethereby eliminated from the external power distribution system. Also thecontinuous power consumption enables the external electrical equipmentto be operated at higher average loading with a resultant increase inefficiency and optimum utilization of the external system apparatus.

The apparatus has been described as being in an upright position withthe central axis of the furnace being vertically aligned. It is to beunderstood that in actual use the apparatus may be modified to operatewith the work path axis and the induction coil axis in alignedhorizontal or inclined positions. It is to be further understood thatthe form of our invention, as shown and described, is to be taken as apreferred example of the same, and that various other changes andmodications '"6 may be resorted to without departing from the spirit andscope of the invention.

We claim as our invention:

l. In an induction furnace having a workpiece pathway for electricheating of hollow metallic workpieces, the combination of an open-coretransformer having at least one outer core leg and at least one innercore leg, a coil mounted therebetween, a fluid pressure operatedworkpiece carrier having a first position and a second position, and aplurality of magnetizable flux concentrating core members mounted formovement with said carrier, said first position being such that saidcore members are axially spaced from said core legs to allow loading ofa workpiece on said carrier between said core legs and said carrier,said second position being such that said workpiece is locatedconcentrically within said coil and said core members are disposed inthe workpiece pathway adjacent to said core legs to substantially closethe magnetic circuit of said open core transformer.

2. In a furnace for electrical heating of workpieces, the combination ofa transformer of the open-core type having a plurality of outer core legmembers and a corresponding plurality of inner core leg members with acoil mounted therebetween, a support for said transformer having asubstantially planar table top, said transformer being mounted on saidsupport in spaced relation above said table top, a workpiece elevatingmechanism mounted on said support below said table top, a workpiececarrier connected to said elevating mechanism for vertical movementrelative thereto to a raised position, a plurality of auxiliary coremembers mounted for movement with said elevating mechanism and normally1ocated below the plane of said table top, said auxiliary core membersbeing positioned when said workpiece carrier is in said raised positionto substantially complete the magnetic circuit of said open-coretransformer.

3. In an electric induction furnace having a substantially cylindricalwork path and further having an induction coil concentricallysurrounding a portion of said work path for inductively heating aworkpiece having side walls, the combination of a first plurality ofperipherally spaced core members adjacent the outside of said coilhaving an elongated dimension parallel to the axis of said work path, asecond plurality of core members within said work path correspondingindividually to and aligned in parallelism with said rst core members, amovable group of auxiliary core pieces mounted one beside another in aplane spaced axially from the end of said coil and circumferentiallyfollowing the end of said workpiece, said group being mounted formovement from a iirst position to a second position, a reciprocablepusher member for moving a workpiece to be heated axially into said coilwith said sidewalls between said rst core members and said second coremembers, said group of auxiliary core pieces being mounted for movementwith said pusher member from said iirst position to said secondposition, said second position being such that the individual corepieces of said group are effective to substantially decrease the air gapbetween the ends of corresponding core members of said first pluralityand said second plurality.

4. In an induction heating apparatus having a first work station and asecond work station and having an induction coil concentricallysurrounding the second work station for heating the sidewalls ofmetallic workpieces, the combination of a plurality of substantiallyU-shaped magnetizable core members straddling the periphery of said coilwith inner legs of each core member projecting downwardly within saidcoil, a first elevating means for bringing the sidewall of the workpieceto be heated into inductive relation within said coil between said coiland said downwardly projecting core members and are retractably removingit therefrom, a plurality of auxiliary magnetizable core membersradially spaced from the axis of said work stations and asecond'elevatiug means` supd porting said auxiliary core members for.axial movement to a position substantially adjacent the outerlegsfof'said Uv-shaped'members so as Vto decrease the air gap betweensaid outer legs and said innerlegs. y

5. In combination with lan elongated cylindrical inductor coil forheating of hollow cylindrical Workpieces having sidewalls, a pluralityof substantially U-shaped core members straddling the inductor coil andspaced around the circumference of the coil each -having an outer legmember adjacent the outside of said coil and anV inner `leg memberspaced 'from the inside of said coil, anda plurality of auxiliary corepieces individuallyspaced from the open ends .of said core members iandsupported for reciprocal movement axially toward and away from saidU-shaped core members, lst elevator means for reciprocally moving Vaworkpiece axially into said `inductor coil with said'workpiece sidewallsbetween said inner Yleg members and ,said outer leg members, and secondelevator means for moving said auxiliary core pieces to a position`adjacent the ends of said inner and outer leg members, said positionbeing such that each of said core pieces is efective to substantiallycomplete the magnetic circuit between one of said outer leg members andthe corresponding inner leg member.

combination of a first plurality of peripherally spaced outer core jlegmembers positioned adjacent the outside of said coil, a second pluralityof inner core leg members spaced fromV the inside Voiisaid'coil andsubstantially parallel to`said outer core members, anda plurality ofauxiliary core pieces movably supported in a firstv position spacedaxially from the end of said coil and reciprocally movable to a secondposition adjacent the ends of ,said outer'core members, said secondposition being such that said auxiliary core pieces are eiective todecrease the reluctance of the magnetic flux path between the ends ofsaid outer core members and said inner core members.

References Cited in theiilre of kthis patent Y UNITED STATES PATENTS2,337,258 Limpel ,Dec. 21, 1943 2,359,285 Bennett Oct. 3, 1944Y2,363,994 Richter NOV. 28, 1944

